This invention relates generally to a precompression pump sprayer of the type in which a discharge valve seat, carried by the main piston, is opened upon a build-up of pressure in the pump chamber and is closed when that pressure is overcome by the force of a spring moving a valve member into its closing position. When the discharge passage is open, the fluid inlet to the pump chamber is closed, and while the discharge passage is being closed, the fluid to the chamber is reestablished.
U.S. Pat. No. 4,051,983 discloses a precompression pump sprayer of the class described in which the discharge valve forms a sub-assembly of three parts including a valve rod, a secondary piston operating in a secondary portion of the pump cylinder, and an inlet ball check valve, the sub-assembly moving together as a unit during the pressure and suction strokes of the main piston for controlling discharge and inlet passages from and into the main pump chamber as in the known pressure build-up sprayers of this type. The pump chamber is primed by expelling unwanted air therefrom directly into the container through the dip tube near the end of the downstroke of the sub-assembly, such that the expelled air is replaced by liquid from the container on each ensuing upstroke.
This three-part sub-assembly requires an additional part for the overall pump assembly which adds to the cost, and a sub-assembly operation and equipment are required which further increase time and expense.
The piston return spring is housed in a separate chamber beneath the subassembly which, during the process of priming the pump, collects liquid and expelled air from the pump chamber and tends to retard the priming ability of the pump.
This retarding effect is enhanced especially for viscous and difficult to prime liquids, thereby increasing the number of strokes-to-prime factor. Besides, the return spring housing of the U.S. Pat. No. 4,051,983 pump sprayer is in direct communication with the dip tube such that the return spring after priming is fully immersed in liquid product which may over time reduce the efficiency of the return spring or may cause contamination of the spring and/or liquid product itself.
British patent 2,051,969 discloses a precompression pump sprayer which includes a single piece member forming a discharge valve on one end and a secondary piston at its opposite end operating in a counterbore formed by an insert defining a secondary cylinder. This secondary cylinder forms a separate return spring housing in direct communication with the interior of the container via a separate air flow passage. The inlet check valve is located beneath the insert, and a separate product flow passage from the valve controlled inlet is established directly into the pump chamber through an outer groove formed in the side and bottom walls of the insert.
It is the objective of this prior art pump according to the British patent to isolate the return spring housing from the liquid flow path into the pump chamber, and to reduce any resistance or head loss which would retard pumping movement due to air within the spring chamber.
The pump structure according to this prior art sprayer gives rise to several disadvantages. Either a separate insert defining the spring housing must be provided, requiring a separate part which adds to the cost and is difficult to assemble, or should the insert to be formed integrally with the pump housing, an elongated bore must be molded in the housing wall to establish direct communication with the pump chamber, which is difficult and costly to mold.
Moreover, the spring chamber varies in volume during pump reciprocation, such that the column of air in the spring housing could retard movement of the discharge valve during the pump pressure stroke, and the expanding volume of the spring housing during the pump suction stroke could cause container collapse or hydraulic lock of the secondary piston during the suction stroke, unless product suctioned from the container is adequately replaced by atmospheric air through the container vent.
Besides, strokes-to-prime issues are not contemplated by this disclosure, as no pump priming means is even disclosed.
Moreover, neither of the aforedescribed pumps has the ability to regulate the rate at which the discharge is opened and closed by controlling the rate of reciprocation of the discharge valve/secondary piston during the pump operation.